Merck Manual

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Baker Cysts

(Baker's Cysts; Popliteal Cysts)


Deepan S. Dalal

, MD, MPH, Brown University

Reviewed/Revised Apr 2022 | Modified Sep 2022

Baker cysts are small sacs filled with joint (synovial) fluid that form in an extension of the joint capsule behind the knee.

A Baker cyst results from an accumulation of trapped joint fluid, which bulges from the joint capsule behind the knee as a protruding sac. Causes of the joint fluid accumulation include rheumatoid arthritis Rheumatoid Arthritis (RA) Rheumatoid arthritis is an inflammatory arthritis in which joints, usually including those of the hands and feet, are inflamed, resulting in swelling, pain, and often destruction of joints.... read more Rheumatoid Arthritis (RA) , osteoarthritis Osteoarthritis (OA) Osteoarthritis is a chronic disorder that causes damage to the cartilage and surrounding tissues and is characterized by pain, stiffness, and loss of function. Arthritis due to damage of joint... read more Osteoarthritis (OA) , other inflammatory joint diseases and overuse of the knees. Baker cysts often cause discomfort at the back of the knee but often do not cause symptoms. The cysts may enlarge to the size of a baseball and extend downward into the calf muscles.

A rapid increase in the amount and pressure of fluid within the cyst can cause it to rupture. The fluid released from the cyst can cause the surrounding tissues to become inflamed, resulting in symptoms that may mimic those of a blood clot in the calf (deep vein thrombosis [DVT] Deep Vein Thrombosis (DVT) Deep vein thrombosis is the formation of blood clots (thrombi) in the deep veins, usually in the legs. Blood clots may form in veins if the vein is injured, a disorder causes the blood to clot... read more Deep Vein Thrombosis (DVT) ). Moreover, a bulging or ruptured Baker cyst can rarely actually cause thrombophlebitis in the popliteal vein (which is located behind the knee) by pressing on the vein.

Diagnosis of Baker Cysts

Treatment of Baker Cysts

  • Nonsteroidal anti-inflammatory drugs (NSAIDs)

  • Joint or cyst aspiration and corticosteroid injection

  • Sometimes surgical removal of the cyst

When arthritis causes chronic knee swelling, the doctor may need to remove the fluid with a needle (a procedure called joint aspiration Joint aspiration (arthrocentesis) A doctor can often diagnose a musculoskeletal disorder based on the history and the results of a physical examination. Laboratory tests, imaging tests, or other diagnostic procedures are sometimes... read more Joint aspiration (arthrocentesis) ) and inject a long-acting corticosteroid (such as triamcinolone acetonide) to reduce the size of the cyst or prevent the formation of a Baker cyst. The doctor may also aspirate and inject the cyst. Removing the cyst surgically is an alternative if other treatments are not effective.

Sometimes cysts rupture and the cyst fluid is reabsorbed by the body. If the cyst has ruptured, the pain is treated with an NSAID or another pain reliever. If the ruptured cyst causes thrombophlebitis in the popliteal vein, treatment is bed rest, elevation of the leg, warm compresses, and anticoagulants (such as warfarin).

Drugs Mentioned In This Article

Generic Name Select Brand Names
Aristocort, Aristocort A, Aristocort Forte, Aristocort HP, Aristo-Pak, Aristospan, Azmacort, Children's Nasacort Allergy 24HR Nasal Spray, Cinalog, Cinolar, Flutex, Hexatrione, Kenalog, Kenalog in Orabase, Kenalog-10, Kenalog-40, Kenalog-80, Nasacort, Nasacort AQ, Oralone, SP Rx 228 , Tac-3 , Triacet , Triamonide , Trianex , Triderm , Triesence, XIPERE, Zilretta
Coumadin, Jantoven
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